Mitsubishi Montero: Bad Spark Plugs → Symptoms and Diagnosis

Bad Spark Plug Symptoms Mitsubishi Montero

Bad spark plugs can cause many problems with your Mitsubishi Montero.  Bad spark plug symptoms may be subtle, or incredibly noticeable.

The basic design and task of the spark plug has changed little over the last 100 years.  They sit on top of the combustion chamber and ignite the air/fuel mixture and start the power stroke of the engine.

Something that has changed about modern spark plugs is that many of them use iridium, don’t need gapped, and can last for 100k miles with little issue.  That being said, they still can go bad.  The good news is, that if you do need replace them all, they are very affordable.

 

Common Bad Spark Plug Symptoms:  Mitsubishi Montero

There are a lot of potential symptoms related to bad spark plugs in your Montero.  We always recommend using an OBDII scanner to pull your trouble codes if you have a check ending light on.  It can really narrow your search down.  If you don’t have one, your local parts store will do this for you for free.

It is also worth noting, that the symptoms of bad spark plugs will be almost the same as any other bad part in the ignition process.  This means that something such as bad coil packs will produce the same results and feel as bad plugs.

Mitsubishi Montero Bad Spark Plug Symptoms
On the left is a fouled spark plug. on the right is the exact same type of plug new.

 

Check Engine Light

The check engine light is one of the most common symptoms of bad spark plugs. More often than not, your engines computer will be able to detect bad spark plugs in your Montero. 

There are several misfire related trouble codes.

  • P0300–  this trouble code indicates that there is a random misfire. A random misfire means is that a misfire is detected, but the ECM is not able to determine which one it is coming from, or the misfire is occurring randomly.
  • P0301 through P0312-  these trouble codes indicate that there is a misfire in one specific cylinder.  For example, P0304 is for a misfire in cylinder 4 in the firing order.  This makes diagnosing the misfire a bit more straightforward.

There are other misfire related codes as well. 

 

Accelerates Slower than Normal

As you ask your Montero for more power, the fuel and ignition systems respond.  If acceleration has diminished, it should be felt.  The less cylinders that your engine has, the more that one cylinder not firing properly will have.  If you have one or more bad spark plugs, it’ll cause the acceleration of the Montero to be weaker.

 

Fuel Economy

The less efficient the combustion of your engine, the more fuel is going to be wasted.  This leads to a decrease in fuel economy.  When you take your vehicle in for a tune up due to decreased fuel economy, checking the spark plugs (and ignition system in general) is going to be one of the very first places that a mechanic is going to look at.

 

Misfire

Misfiring is the most common symptom of bad spark plugs.  All of the other symptoms are a result of the misfiring itself.  The real question is, what is causing the misfire?  There is more to your Montero’s ignition system than just the plugs.  There’s also coil packs and spark plug wires.

There are also non ignition related circumstances that can cause a misfire.  That would include lack of fuel pressure, bad fuel injectors, or even a timing chain (or belt) that has jumped.  Since there are so many reasons that a vehicle can misfire, we recommend testing for trouble codes first.

Here’s a good video from YouTube on identifying a bad spark plug.

 

Rough Idling

When a spark plug is misfiring, it is often most pronounced at idle speed.  This is because when the engine turns slower, it is easier to detect.  You’ll feel a rough vibration.

 

Conclusion:  Bad Spark Plugs Mitsubishi Montero

Be aware that almost all symptoms of a bad spark plug in your Montero could also be other issues with the ignition system as well.  Good luck diagnosing the problem  Feel free to leave a comment below if there is anything that you would like to add.